1. Field of the Invention
This invention relates to solid or liquid fertilizers containing urea to which urease inhibitors are added.
2. Description of the Prior Art
Urea and commercial fertilizers containing urea are used in solid form as soil fertilizer and in liquid form as both soil and leaf fertilizer. The enzyme urease catalyzes the hydrolysis of urea according to the following reaction equation: ##STR4##
The reaction frequently proceeds so quickly that:
in soil fertilization, particularly on low-sorption and dry soils, a portion of the ammonia freed from the soil can no longer be bonded and escapes into the atmosphere. As a result, substantial quantities of nitrogen which could be utilized by plants are lost. PA1 in leaf fertilization, ammonia quickly occurs in such high concentrations that it can lead to leaf damage and, in part, also be released into the atmosphere. PA1 20 kg/ha N in the form of urea solution or PA1 40 kg/ha N as ammonium nitrate-urea solution (AUS)
In general, the threshold value from which point such damage occurs with grains, is at
To prevent such damage to leaves, it is frequently necessary, in the case of leaf fertilization with fertilizers containing urea, to remain below the dosing level of 60-80 kg/ha N necessary for optimal plant yield.
With the aim of reducing such leaf damage, experiments have been undertaken to apply the liquid containing urea in larger droplets. In doing so, a large portion of the sprayed fluid drains off from the leaves so that, for this reason, less damage is observed. At the same time, however, the real advantage of leaf fertilization, namely the direct and therefore rapid absorption of nitrogen possible with fine-droplet application, is lost.
Application of extremely fine droplets is achieved with rotary nozzles. Instead of 200-400 l/ha of sprayed liquid, 20-40 l/h are used. In doing so, a very intensive sprinkling is achieved which is, however, in the event of dry or warm weather, particularly endangered by evaporation (see page 29, paragraph 4 and page 20, paragraph 1).
To avoid the disadvantages associated with the use of solid fertilizers containing urea in soil fertilization, frequent experiments have been undertaken with the application of substances inhibiting the activity of the enzyme urease, thus retarding the hydrolysis, cf., e.g. DL 122 621, DL 122 178 and DL 121 457 as well as Bundy, L. G. and J. M. Bremner in "Soil Biol. Biochem." 6 (1974) 27-30, 369-76 and J. M. Bremner and L. A. Douglas in "Soil Sci. Soc. Am. Proc." 37 (1973) 225-226.
However, to date, attempts to practically apply such urease inhibitors have been unsuccessful. For example, during storage of solutions containing urea, decomposition of the urea repeatedly occurs, adversely affecting storage stability.
Hence, a need clearly continues to exist for additives for both solid and liquid fertilizers containing urea which will produce mixtures which prevent the loss of NH.sub.3 on fields and grassland; are themselves compatible with plants, i.e. do not cause damage; and which bring about enhanced crop yields.